Feasibility of the detection of D 0 mesons in the NA61/SHINE experiment: Vertex detector for NA61/SHINE P. Staszel and Yasir Ali Jagiellonian University Silicon Detector Workshop, Split, 8-10 October 2012

2 Outline 1. Updates on simulation 2. New layout based on MIMOSA -26 VTPC2

3 Vertex Detector (VD) NA61/SHINE detector – top view

4 VTPC2 Outer VDS's dimensions The two following slides (slide 5 and slide 6) summarize calculations used to find the optimal sizes of the VDS's. In these simulations we generated 100 k events that contains only signal: 1 D0 meson decaying is to pi+K pair. The rapidity and m T distributions assumed for the generated D 0 s are the same as these predicted by AMPT for Pb+Pb at 158AGeV. The calculations were performed with relatively large stations. This allowed us to set fiducial cut on each stations. The idea for the cut was to keep the most occupied area within the cut and remove (outer) areas with low occupancy, so finally we obtain high signal acceptance using relatively small stations. The figures show hit (x,y) distributions generated by signal tracks is Vds1 – Vds4. The dashed boxes represent the cuts. We found that in Vds1 ~99.5% of signal tracks is localized within the box 2x4cm 2. As you can see to cover the remaining 0.5% we would need to extend the cut in the x direction for almost factor of 2. For stations Vds2-Vds4 we just extend size of the boxes in proportion to their distance from the target. So we got dimensions: 4x8cm2, 6x12cm2 and 8x16cm2 for Vds2, Vds3 and Vds4, respectively. You can see the signal lost is kept below 1 % for each station. For Pb+Pb at 40 AGeV the signal lost is on the level of 4% for the same cuts.

5 Signal track distribution at 158 AGeV in VDS1 and VDS2 VTPC1 VTPC2 4x8 cm 2 2x4 cm 2

6 VTPC1 VTPC2 Signal track distribution at 158 AGeV in VDS3 and VDS4 6x12 cm 2 8x16 cm 2

7 Comments to slides 9-15 VTPC1 VTPC2 Slide 9 reminds us that for central Pb+Pb at 158AGeV we can expect very high hit occupancy on the level of 5 hit/mm 2 /event in the most inner part of the vertex detector. It suggest that silicon pixel sensors would provide a good solution for us. The following conceptual drawings are based on MIMOSA-26 chip hosting sensitive area of about 1.06 x 2.12 cm 2 with the pixel pitch equal 18.4 μm (~663.5k pixels/chip): These pads are for testing purpose and can be removed

8 Comments to slides 9-15 VTPC1 VTPC2 The chips are available. We can just by them at IPHC, Strasbourg (we know also the estimated price per chip) We assume that each Vds station will have a inner hole to let the beam go through. The chosen shape is a square with dimension of 6x6 mm 2. Moreover we assume, than the sensitive part of VDS should cover the area defined by the dashed boxes from slide5 and slide6. Because Vds1 and Vds2 seems to have a relatively small surfaces we propose to make these two stations only of pixels. It will provide not only a very good two track separation but will also ensure that we have the same vertex reconstruction accuracy in the whole phase space. This accuracy is defined mostly by the 2 most forward stations (Vds1 and Vds2). For Vds3 and Vds4 we propose the use inner pixel rings - as the hit occupancy in the inner part is still large. The external areas will be cover by a thin MicroMegas detectors with the indicated dimensions (see next slides). Slides show the conceptual drawings for the individual stations. I stored all the stations on slide14 to give us an idea of how the whole VD will look like. IPHC

9 1. VTPC1 VTPC2 Charged particles produced in Pb+Pb 0-10% central interactions 13mm

VTPC1 VTPC2 Preliminary drawing of the 1-st station Drawn blue boxes have dimensions of the sensitive area of MOMOSA-26 sensor (~1x2cm 2 ) Size of the dashed box is ~ 2x4 cm 2. We have to cover this area to loose less than 0.5% / 3% of signal particles for 158 / 40 GeV

VTPC1 VTPC2 Preliminary drawing of the 2-nd station MOMOSA-26 sensors (~1x2cm 2 ) Size of the dashed box is ~ 4x8 cm 2 – same meaning as for Vds1 Full coverage with MOMOSA sensors Vds2

VTPC1 VTPC2 Preliminary drawing of the 3-rd station Inner ring – same layout as Vds1 based on MIMOSA-26 Outer region covered with thin MicroMegas: MM_A with dimension 2.3x4.7 cm 2 MM_B with dimension 4.7x6.3 cm 2 Size of the outer dashed box is 6x12 cm 2 MM_B MM_A

VTPC1 VTPC2 Preliminary drawing of the 4-th station Inner ring – same layout as Vds1 based on MIMOSA-26 Outer region covered with thin MicroMegas 6 MM_B stations (4.7x6.3 cm 2 ) → only 2 types of MicroMegas detectors have to be developed → eventually MM_A in Vds3 can be replaced with MM_B → only one type of MM MM_B 16cm 8cm

VTPC2 Preliminary drawing of the complete VD

15 Inner pixel rings of Vds3 and Vds4 VTPC1 VTPC2 As mentioned on the previous slides Vds3 and Vds4 inner rings will be identical with Vds1. This will minimize the number of designs. The following slides show drawings of the stations together with the simulated hit occupancies. You can see that using the proposed solution the most hot areas cover by MicroMegas will have <0.5 hit/mm 2 /event which seems to be feasible for these kind of detectors (need to check it out with L. Ropelewski)

VTPC1 VTPC2

VTPC1 VTPC2

18 Backup Slides

VTPC1 VTPC2 D 0 → K + π -, 200k 0-10% cent. Pb+Pb at 158 AGeV S/B=13 For 50M events: SNR = k D 0 +D 0 bar S/B=15 For 50M events: SNR = k D 0 +D 0 bar S/B=6.6 For 50M events: SNR = k D 0 +D 0 bar S/B=9.6 For 50M events: SNR = k D 0 +D 0 bar